The present invention relates to production of vitamin K.sub.1 and vitamin K.sub.2. More specifically, the present invention relates to a process for producing precursors for the above mentioned vitamins K.sub.1 and K.sub.2, which precursors are converted into the vitamins by oxidation, by alkylating 2-methylhydronaphthoquinone-1,4 with a specified alkylating agent.
Heretofore, it has been known that, in general, vitamin K.sub.1 can be prepared by condensing 2-methylhydronaphthoquinone-1,4 with phytol, isophytol or derivatives thereof with heat in an organic solvent in the presence of an acid catalyst such as oxalic acid or boron trifluoride etherate to produce a hydroprecursor and oxidizing the hydro-precursor with an inorganic oxidizing agent such as manganese dioxide or silver oxide to convert it into vitamin K.sub.1. However, a problem accompanying this process is that it provides a very low yield of vitamin K.sub.1 because 2-methyl-2-phytyl-2,3-dihydronaphthoquinone-1,4 is produced as a by-product in a quantity approximately equal to that of vitamin K.sub.1.
In order to overcome the above mentioned drawback, acylation has been carried out in the hydroxyl group of the 1-position to prevent the formation of the by-product. However, this process is accompanied by a problem in that the synthesis of 4-acyloxy-3-methyl-1-naphthol requires complicated procedures and provides a low yield, and the resulting condensation product must by hydrolysed with an alkali because it is in the form of a half ester. For the same purpose, there has also been proposed a process using 2-methyl-1,4-naphthohydroquinoneditetrahydro-pyranylether. In this process, the yield of vitamin K.sub.1 is not very high in spite of the use of an expensive protective group 2,3-dihydropyran, and the dehydration of the solvent used and the purification of the catalyst used must be carefully carried out.
Additionally, it is known that vitamin K.sub.2 (10) can be synthesized by condensing a monopotassium salt of 2-methylhydronaphthoquinone-1,4 with geranyl bromide with heat in toluene as a medium. This process requires complicated operations and, as in the case of the acid catalyst reaction, produces a by-product, 2-methyl-2-geranyl-2,3-dihydronaphthoquinone-1,4, with the result that the yield is as low as 20%.
Moreover, there has been proposed a process comprising condensing a halide of 2-methyl-1,4-dialkoxynaphthalene in the presence of a .pi.-allylnickel complex and a process comprising synthesizing metaloquinone from 2-methyl-1,4-dialkoxynaphthalene and condensing the metaloquinone with an allyl halide. All these synthetic processes entail a large number of steps and require the absence of water, thereby requiring accurate control of operations.